I find it very hard to believe that a splash from a passing car could hydrolock an engine. The biggest detriment to water actually making it to the cylinders is the air filter, which does not easily pass water. If it got a big splash, sure some water would make it to the cylinders in the form of a mist and vapor, but not a slug large enough to do something. Especially on a gas engine where the air intake is usually lower than the manifold.

I'd suspect there's more to the story that hasn't been said.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

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1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]